Automatic injection devices

ABSTRACT

An injection device comprises a syringe extendible against a spring bias from a retracted position in a housing to a projecting injecting position. A spring biased plunger has collapsible elbows which, when the plunger is released, initially engage the end of the syringe to drive it to the projecting position, whereupon arresting of the syringe movement causes the elbows to collapse inside the syringe to allow the plunger to engage and drive the bung.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/630,507 filed Jan. 7, 2008, which is a '371 of PCT Patent ApplicationNumber PCT/GB2005/002487, filed Jun. 23, 2005, which claims priority toUnited Kingdom Patent Application No.: 0414054.7 filed on Jun. 23, 2004.The entire contents of each of the above applications are hereinincorporated by reference in their entirety.

BACKGROUND

There are various forms of automatic injection device which whenoperated cause the needle of a syringe to be moved forwardly so that itprojects from a protective housing prior to actuation of the syringe toexpress a dose of liquid through the needle. It is important to try toensure that the syringe is moved bodily forward to expose the needlebefore the liquid charge is pressurised so that dribbling from theneedle does not occur before the actual injection takes place. It is anobject of this invention to provide a mechanism which operates in thisdesired manner.

SUMMARY

According to the invention there is provided an injection device forcausing a dose of liquid to be ejected from the needle at one end of asyringe located within a housing of the device, the syringe beingmovable by a plunger, upon release of an actuating bias member at oneend of the housing, to move the syringe, from a first position whereinthe needle is shrouded by the housing, to a second position wherein theneedle projects from the other end of the housing, the plunger being inthe form of a rod with a longitudinally centrally located flexibleprojecting portion which, prior to release of said actuating biasmember, is situated beyond the other end of the syringe, such that aprimary movement of the plunger, under the bias of the actuating biasmember, will cause the projecting portion to bear against the other endof the syringe such that the syringe is moved from said first to saidsecond position, whereupon arresting of further movement of the syringe,results in the flexible portion collapsing inwardly so that it entersthe syringe, thus enabling the plunger to move by a secondary movement,within the syringe, into contact with and to act upon a plug to compressthe liquid within the syringe and cause expression of the liquid throughthe syringe needle.

With such an arrangement, the projecting portion will remain in itsprojecting position (in order to move the syringe from the first to thesecond position) until the force increases to such an extent whichallows the projecting portion to collapse inwardly so that the plungercan then move within the syringe to cause the liquid to be expressedthrough the syringe.

The projecting portion can comprise one or more flexible elbowsprojecting beyond the normal circumference of the rod, but compressibleinto said circumference. This could be in the form of two elbows definedeither side of a longitudinal slit or central void in the rod. Theelbows could be pre-formed as a pair of arms either side of thelongitudinal slit between upper and lower solid portions of the rod.

Preferably the injection device will contain a return bias member actingbetween the syringe housing and the other end of the syringe to hold thesyringe retracted within the housing until the actuating bias member isreleased. One or more of the bias members provided within the housingcan be in the form of a coil spring.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be performed in various ways and a preferred examplethereof will now be described, with reference to the accompanyingdiagrammatic drawings, in which:

FIG. 1 is a sectional view through an injection device of this inventionprior to use; and

FIGS. 2 and 3 are similar views showing successive stages of operationof the injection member.

DESCRIPTION

The injection device shown in the drawings comprises a syringe 1 locatedwithin a protective housing 2. The syringe comprises a 3 incorporating aliquid dose held in place by a bung 4 and having a needle 5 throughwhich the dose can be ejected by applying pressure to the bung 4. The 3has an enlarged head 6. A plunger 7 is biased forwardly by a coil spring8, but is held back in a latched position (FIG. 1) until such time as atrigger shown schematically at 11 is actuated to release the plunger andthe spring 8. Prior to use the syringe 1 is held retracted in thehousing 2 by a coil spring 9.

It will be seen that the plunger 7 is in the form of a rod having acentral portion which defines a pair of projecting elbows 10. These canbe pre-formed as part of a moulded plunger 7. The projecting elbowportions 10 are flexible so that they can be moved inwardly to causethat portion of the rod to adopt a circumference similar to that of therest of the rod. As can be seen in FIG. 2, when the plunger is releasedand biased by the spring 8 the expanded region formed by the elbows 10rests against the head 6 of the 3 and the force provided is sufficientto compress the spring 9 until such time as the head 6 abuts the top ofthe housing 2, whereupon further movement of the 3 is arrested. Thecontinual bias created by the spring 8 then causes the elbows 10 to be20 compressed inwardly as they enter into the interior of the 3. Withthe elbows 10 in the collapsed state, the plunger can then moverelatively easily within the 3 so as to act upon the bung 4 and thuscause the contents of the syringe to be ejected through the needle 5.

The illustrated configuration of the plunger 7 provides severaltechnical advantages. It can be moulded integrally. Also the collapsingmovement of the projecting elbows provides an arrangement which canprovide a suitable injection force to cause the needle to enter the skinto a suitable depth, but then provide a relatively low drag against theinner wall of the syringe container so that the major portion of thethrust of the spring for the remainder of its stroke is applied to thebung 4. It will be appreciated that other configurations of collapsingprojection could be used in place of the collapsing elbows.

1. An injection device, comprising: a housing; a syringe coupled to aneedle at one end, the syringe slideably mounted within the housing formovement between a first position relative to the housing in which theneedle is shrouded by the housing and a second position relative to thehousing in which the needle projects from the housing; a bung slideablymounted in the syringe and moveable to expel a liquid through theneedle; a plunger comprising: an upper solid portion, a lower solidportion having one end operable to move the bung and to transmit anexpulsion force thereto, and a projecting region comprising one or moreflexible elbows on either side of a central void provided between theupper and lower solid portions of the plunger, the plunger having afirst length when the projecting region is in a projecting position inwhich the one or more elbows project outwardly from the central void,the plunger having a second length greater than the first length whenthe projecting region is in a collapsed position in which the one ormore elbows are collapsed inwardly toward the central void; and anactuating bias member provided at one end of the housing and operable tomove the plunger toward another end of the housing.
 2. The injectiondevice as claimed in claim 1, wherein the projecting region of theplunger is configured to drive the syringe from the first positionrelative to the housing to the second position relative to the housingsuch that the needle projects from the housing.
 3. The injection deviceas claimed in claim 1, wherein the projecting region of the plunger isin the projecting position prior to entering the syringe and wherein theprojecting region is in the collapsed position inside the syringe forapplying the expulsion force to the bung in order to compress the liquidin the syringe and cause expression of the liquid from the syringe,wherein a collapsing movement of the projecting region toward thecentral void from the projecting position outside the syringe to thecollapsed position inside the syringe causes elongation in the length ofthe plunger from the first length to the second length.
 4. The injectiondevice as claimed in claim 1, wherein the central void is alongitudinally extending slit.
 5. The injection device as claimed inclaim 1, further comprising: a return bias member acting between thehousing and another end of the syringe to hold the syringe in the firstposition relative to the housing until the actuating bias member isreleased.
 6. The injection device as claimed in claim 1, wherein one ormore of the bias members provided within the housing is in the form of acoil spring.
 7. The injection device as claimed in claim 1, wherein thehousing is fixed relative to the syringe.
 8. The injection device asclaimed in claim 1, wherein the plunger is molded integrally.
 9. Asyringe assembly, comprising: a syringe coupled to a needle at one end,the syringe slideably mounted within a housing for movement between afirst position relative to the housing in which the needle is shroudedby the housing and a second position relative to the housing in whichthe needle projects from the housing; a bung slideably mounted in thesyringe; and a plunger comprising: an upper solid portion, a lower solidportion having one end operable to move the bung and to transmit anexpulsion force thereto, and a projecting region comprising one or moreflexible elbows on either side of a central void provided between theupper and lower solid portions of the plunger, the plunger having afirst length when the projecting region is in a projecting position inwhich the one or more elbows project outwardly from the central void,the plunger having a second length greater than the first length whenthe projecting region is in a collapsed position in which the one ormore elbows are collapsed inwardly toward the central void.
 10. Thesyringe assembly as claimed in claim 9, wherein the projecting region ofthe plunger is configured to drive the syringe from the first positionrelative to the housing to the second position relative to the housingsuch that the needle projects from the housing.
 11. The syringe assemblyas claimed in claim 9, wherein the projecting region of the plunger isin the projecting position prior to entering the syringe and wherein theprojecting region is in the collapsed position inside the syringe forapplying the expulsion force to the bung, wherein a collapsing movementof the projecting region toward the central void from the projectingposition outside the syringe to the collapsed position inside thesyringe causes elongation in the length of the plunger from the firstlength to the second length.
 12. The syringe assembly as claimed inclaim 9, wherein the central void is a longitudinally extending slit.13. The syringe assembly as claimed in claim 9, wherein the housing isfixed relative to the syringe.
 14. The syringe assembly as claimed inclaim 9, wherein the plunger is molded integrally.
 15. A method foroperating an automatic injection device, the method comprising:operating an actuating bias member to move a plunger including aprojecting region comprising an upper solid portion, a lower solidportion and one or more flexible elbows on either side of a central voidprovided between the upper and lower solid portions of the plunger,wherein the projecting region is in a projecting position when the oneor more elbows project outwardly from the central void and in acollapsed position when the one or more elbows are collapsed inwardlytoward the central void; and engaging one end of a syringe with theplunger to drive the syringe from a first position relative to a housingin which a needle coupled to another end of the syringe is shrouded bythe housing to a second position relative to the housing in which theneedle projects from the housing; wherein the projecting region of theplunger is in the projecting position prior to entering the syringe andwherein the projecting region is in the collapsed position inside thesyringe for applying an expulsion force to a bung in the syringe inorder to compress a liquid dose in the syringe and cause expression ofthe liquid dose from the syringe, wherein a collapsing movement of theprojecting region toward the central void from the projecting positionoutside the syringe to the collapsed position inside the syringe causesan elongation in the length of the plunger.
 16. The method as claimed inclaim 15, wherein the central void is a longitudinally extending slit.17. The method as claimed in claim 15, further comprising: holding thesyringe in the first position relative to the housing using a returnbias member acting between the housing and another end of the syringe,until the actuating bias member is released.
 18. The method as claimedin claim 15, wherein the housing is fixed relative to the syringe. 19.The method as claimed in claim 15, wherein the plunger is moldedintegrally.